Tuning forks,. Not an expert here but this is basic structural resonant frequency, Pitch goes up with stiffness, down with weight. Your CF fork is lighter and stiffer.

And yes, I have observed the relative discomforts on rough roads many times. At Cycle Oregon, those of us riding traditional bikes have learned that we need to expect the rapid slowdown when the pavement turns rough. THose slowing are on CF bikes.

Now, steel forks can also be too stiff. My Mooney's original fork was designed to be stiff enough touring. Too stiff all the rest of the time. I never felt "planted" going around corners on steep, rough descents. The new fork was made from the same blades, but using the narrow end of the taper instead of the stiff end. Much less stiff and a far better, more secure ride. (I wish I knew where my old fork is. I'd love to compare the frequency with the new next time the new is off the bike. New - as in 1984.)

Ben